A “power supply” is a circuit that provides energy to an electrical or electronic device. Power supplies used in modern electronic equipment include batteries, Direct Current (DC) supplies, Alternating Current (AC) supplies, etc. An example of a modern power supply is the Switched-Mode Power Supply (SMPS). In general terms, an SMPS is used to supply a regulated output voltage to a load, often at a level different than the SMPS' input voltage.
Typically, an SMPS includes circuitry configured to apply a voltage to the gate of a transistor in a switching fashion and with a given duty cycle (i.e., the ratio of on-to-off time), such that the SMPS' duty cycle regulates the output voltage. In operation, because the transistor spends most of its time switching between its two lowest dissipation states (“full on” and “full off”), less energy is wasted. Nevertheless, load disturbances that are characteristic of certain types of integrated circuits (e.g., microprocessors, microcontrollers, etc.) can still cause the output voltage of an SMPS to change in an undesirable manner. Hence, in an attempt to allow the SMPS to more quickly catch up to sudden load variations, hybrid SMPSs have been developed that are capable of operating in linear and hysteretic modes.
In a hybrid SMPS, when the output voltage is between a high threshold value and low threshold value, load variations are dealt with by linearly increasing or decreasing the SMPS' duty cycle. Then, if the output voltage reaches either the high or low threshold values, the SMPS operates in hysteretic mode. Specifically, in hysteretic mode, when the output voltage reaches the high threshold value, the duty cycle is changed to the lowest defined value (e.g., 0%). Conversely, when the output voltage reaches the low threshold value the SMPS applies its highest defined duty cycle (e.g., 100%). As such, a hybrid SMPS may be capable of steering its output voltage back to a suitable value within its linear operating range following a load disturbance.
The inventors hereof have determined, however, that the transition from hysteretic to linear mode in a hybrid SMPS may not be well behaved. For example, when the SMPS returns to linear mode after having operated in hysteretic mode, the output voltage may still be in a transient state and may reach either the high or low threshold values soon thereafter, thus promoting a persistent oscillation between linear and hysteretic modes (referred to as hysteretic oscillation) that may damage the load or otherwise cause the system to operate sub-optimally.